A bit long but... can't really make a TL:DR.

I don't consider myself a "prepper", and compared to my friends I am not, but I do like to prepare for things however just a little bit "differently" than most.

So take what I am going to say with a grain of salt but...

In my opinion, and where I believe many preppers fail, information gain is the best thing you can have.

For example in a SHTF time, the person who knows how to convert dirty water to clean water is going to have a much better chance of survival in the long term than the one who stores 50 gallons of water.

Sure you can buy water filters, but what if you run out?

I also see a lot of preppers who will have closets/garages/freezers of supplies, but they have no plan for what happens if those supplies are not accessible or in the case of frozen supplies a long term power outage.

I myself have 30 days of supplies for myself and my g/f, but they are only what I consider "basic necessities" that would all fit on my horse and she will still be able to carry one of us if we were to be injured.

So my recommendations generally include:

Power/light:

Unless you live somewhere in the mountains where you may not have to worry about leaving your home (few do), don't worry about building out a whole solar system on your home as a prepping tool, this would be useless if you were to have to leave the area.

A home solar system can help for decreasing your footprint (although not really, but that is an entirely different argument) and for short term issues, but if things get really bad it will be useless for most people.

Instead invest in a few cheap USB batteries, a few mini solar panels, low voltage LED light strip and learn how to wire them.

I mostly get my small panels from cheap products that I find in thrift stores.

Now you will have a portable power source that you can use to charge other devices and light up where you end up staying.

Batteries however will eventually fail, so you should learn how to make your own rechargeable batteries from dead batteries.

Water:

Sure you can store a lot of water but this does no good if you have to leave it behind. You can also buy water filters such as these but eventually they will quit working.

Instead you should learn how to also make your own water filter out of usually readily available materials.

NOTE: You can make your own charcoal if none is available.

Food:

While you may be tempted to store your favorite foods, this can often be your downfall. Keeping a lot of canned food is often recommended, but is useless if you have to leave the area and leave most of it behind.

Instead you should learn more about your local environment and what natural sources are available in your area. Also don't be queasy about what you eat.

Learn how to make the tools you will need to be able to catch your own food, a good start is this article and learn how to find or catch your own food more info here and here

Now you may not think you would never do it, but in a pinch if you are starving cockroach is not bad to eat, also makes for a nearly complete meal

The more you can obtain from your local environment, the less you need to store, making it easier to carry more important stuff you may need.

Communication:

This is one area where I see many people forget about, but in the long term communication is something that you will need. All to often poeple think that they can just use their cell phones, but in a true SHTF moment cell phones will likely be unusable due to either over usage or the system crapping itself.

This is not to say that phones will not have their uses, but communication will likely be one of the few things they will be unusable for.

You can buy expensive handheld ham radios, which may be a good option if you can afford them but many can't. Larger units are also available, but these are often not portable.

I recommend picking up old style CB radios (like this one ) as these will often be more portable and able to be used with a small solar system.

In the eventuality of a SHTF collapse, there are already radio operators who have systems in place to setup a "relay network" for providing long distance communication as part of Project OSCAR and even an eventual "internet over ham" through the AMPRNet system.

With the help of the ham radio operators, anyone with a CB radio will be able to gain access to this system of relays and it may be the only way that you will be able to communicate long distance.

Housing:

Since I live in the mountains, in an old mining area, my plans include going to one of a few caves/old mines that few know of but of course this is not an option for everyone.

Explore your local area, find the "hidden areas". Even if you live in a large city, there may be areas that will be useful for living in a SHTF time that most will not know about. For example, in New York there are many hidden/forgotten tunnels and subway stations.

Sure you can go and buy large expensive tents, but this is not an option for everyone.

Instead invest in a roll of painters plastic or woven poly tarps and extension poles (or make your own) as these will be both more portable than many tents and serve more uses such as for tents, water collection, body bags (it will be needed), bags, and really more than many may think of.

Medication:

Many people have medication requirements, however long term storage of medication is not really a feasible option as these can be hard to (legally) get your hands on in any large supply and many do not have long shelf life.

So a good thing to learn now, before it is needed, is if there are any natural medications that can provide the same benefits as your pharmaceutical medications.

Throughout history, humans have used plants to treat all kinds of illnesses. Today, about 40 percent of our prescription medicines come from plant extracts or synthesized plant compounds.

Many natural plants, both legal and illegal, can be used to derive the same effects as many prescription meds. In a true SHTF period, no-one is going to care about legalities.

I will not provide exact information on this, as it is something that you should research yourself based on your known medication needs and also consult with a doctor.

Information:

While above I have covered many different areas, the one thing that you can not have too much of is information.

Do research, but as many sources of information now available may not be available during a SHTF time you need to also insure that you have access to this information.

I recommend storage of information on SD cards which can then be viewed using your standard cell phone. Information retrieval of your personally stored information will become the most important use of your cell phone after a SHTF moment. The cell phone also has the benefit of being easily rechargeable from even a small solar panel.

Information that I recommend:

1. All of Wikipedia - I know this may seem like a weird thing to have, but it is a good source of random information. If you do not include pictures, revisions, or any other "unneeded data" and download only the pure data content, the size is small enough to fit on a sdcard. More info

2. Survival articles - A good place to begin your collection is here

3. Videos - If you can afford the storage to do so, I recommend videos on various subjects, especially those involving how to build your own equipment from "everyday things". A good place to start is "The King of Random" and "Cody's Lab"

I do not recommend using USB drives, and instead prefer sdcards, as these often have additional power requirements and can limit what you can plug them into. There is also the issue of failure, in which you would lose a lot of information should one fail vs a small bit of information if a sdcard fails.

The more you know, and the more information you have access too, the better chance you will have.

Don't panic:

As can be seen during the current Covid-19 pandemic, one of the worst things you can do is panic during a SHTF time.

Plan ahead and while everyone else is running around like chickens with their heads cut off, you can stay in place until you really need to leave.